fix: guard against null data.user in invite-admin-user Edge Function

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

supabase/functions/invite-admin-user/index.ts

@@ -52,6 +52,13 @@ Deno.serve(async (req) => {
     });
   }
 
+  if (!data?.user) {
+    return new Response(JSON.stringify({ error: 'Invite sent but user data unavailable' }), {
+      status: 500,
+      headers: { ...corsHeaders, 'Content-Type': 'application/json' },
+    });
+  }
+
   return new Response(
     JSON.stringify({ id: data.user.id, email: data.user.email }),
     { headers: { ...corsHeaders, 'Content-Type': 'application/json' } },